1. Field of the Invention
The invention relates in general to image processing. More particularly, this invention relates to a method and apparatus for detecting and separating black and white images from color images.
2. Description of the Related Art
In the processing of images, the ability to detect and separate black-and-white (or called grayscale) images from color images is often desired. Black and white images have different characteristics than color images, and different image processing techniques can be applied to each. Separating black and white images from color images not only facilitates the use of such different techniques, but also improves the processing speed because only one-channel computation is necessary for black and white image processing. In addition, the separation of black and white images from color images saves printing costs because black and white toner can be used for images that are only black and white.
In U.S. Pat. No. 5,729,624, Tanioka discloses an image processing apparatus and method for processing color image signals. The apparatus comprises a first judgment unit for judging whether a pixel of interest belongs to a black line image portion, and outputting a first judgment signal indicating a judgment result, a second judgment unit for judging whether pixels in the vicinity of the pixel of interest belong to a black line image portion, and outputting a second judgment signal indicating a judgment result, and a control unit for controlling recording of the pixel of interest based on the first and second judgment signals outputted from the first and second judgment units. With the apparatus, black lines in a color image are satisfactorily reproduced. The present invention, on the other hand, separates black and white images from color images according to the percentage of color pixels in the whole image, and then evaluates the ratio of color pixels to a combined portion of color pixels and dark pixels. While Tanioka focuses on satisfactorily reproducing black lines in a color image, the present invention allows for the detection and separation of black and white images from color images.